Unsteady Aerodynamic Characteristics of a Transonic Oscillating Cascade with Flow Separation

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The unsteady aerodynamic characteristics of oscillating cascades, in which each blade accompanied a flow separation region on its suction surface, were studied by a series of experiment and numerical simulation. A subsonic compressor cascade and a transonic turbine cascade were adopted as model cases.In the experiment, the unsteady aerodynamic force acting on the blade was measured by the influence coefficient method. Behavior of the blade boundary layer was detected with the output signal from hot-film sensors attached to the blade surfaces.From the results on the compressor cascade, the unsteady behavior of the separation bubble on the oscillating blade was clearly shown, and its influence on the unsteady aerodynamic force I moment was revealed.In the experiment on the transonic turbine, the effect of shock wave oscillation on the blade vibration was found quite important. The shock-boundary layer interaction induced a rapid development of the suction-surface boundary layer as well as the boundary layer separation. A remarkable instability of the blade oscillation was detected in the case of low frequency oscillation.A numerical method for unsteady flow around oscillating blades was developed by which the 2D Navier-Stokes equations including Baldwin-Lomax turbulence model were solved with a TVD scheme. The method was verified to be useful through the comparison of the results with available experimental data.A numerical simulation on the transonic turbine was performed on the assumption of inviscid flow. The mechanism of the vibration instability found in the experiment was investigated in detail with the numerical result. It was revealed that the significant phase change around the shock impingement point on the blade suction surface was the dominant factor of the instability.